This invention relates to a process for preparing free standing polymeric belts and more particularly, to a method of forming a free standing polymeric belt from a dispersion of thermoplastic film forming polymer particles in an organic liquid using an electrodeposition step.
Polymer coatings of thicknesses which are less than about 51 micrometers (2 mils) are typically used in the metal finishing industry to protect the metals from corroding and to give them a decorative appearance. Coatings of thicknesses greater than about 51 micrometers are more difficult to obtain and have application in special areas such as insulating coatings in electrical applications such as dielectric receivers and also for free standing films, such as seamless belts. These thick coatings are more difficult to obtain by conventional processes such as spray or dip coating. These conventional processes require repeated applications of thin coatings to obtain thick films. Other limitations of the spray coating process are high equipment cost for air handling, spray equipment and solvent recovery. Also, this process requires extensive factory space for equipment and processing. For polymer film belts, elaborate handling procedures and machinery are also needed to form and remove the belts after the belt is formed. Thus, fabrication techniques such as spray and dip coating systems encounter sagging, multiple application steps, long curing times, sizable equipment space requirements, high cost and other associated problems.
Most belts normally have a thickness greater than about 254 micrometers (10 mils) and are usually formed by molding or lamination. Molding is carried out in complex and expensive molds. Molded articles contain flashings that require removal to achieve a smooth outer surface. Laminated belts are usually prepared by applying alternate layers of thermoplastic sheets and reinforcing fabrics. These materials are relatively thick and stiff, and not suitable for extended cycling over small diameter pulleys or rolls. Other types of belts have been prepared by welding opposite ends of sheets together to form belts having an undesirable seam which projects above the surface of the belt.
Originally, photoreceptors for electrophotographic imaging systems comprised selenium alloys vacuum deposited on rigid aluminum substrates. These photoreceptors required elaborate, highly sophisticated, and expensive equipment for fabrication. Photoreceptors have also been prepared by coating rigid substrates with photoconductive particles dispersed in an organic film forming binder. Coating of rigid drum substrates have been effected by various techniques such as spraying, dip coating, vacuum evaporation, and the like. Rigid drum photoreceptors limit copier and printer design flexibility, are less desirable for flash exposure and are expensive. Flexible organic photoreceptors in the form of belts have recently become popular. These flexible photoreceptors are manufactured by coating a web and thereafter shearing the web into segments which are then formed into belts by welding opposite ends of the sheared web. The resulting welded seam on the photoreceptor disrupts the continuity of the outer surface of the photoreceptor and must be indexed so that it does not print out during an imaging cycle. In other words, efficient stream feeding of paper and throughput are adversely affected because of the necessity to detect a seam within the length of each sheet of paper. Seam detection is a particularly vexing problem for smaller copier and printer designs. The mechanical and optical devices required for indexing add to the complexity and cost of copiers, duplicators and printers, and reduce the flexiblity of design. Welded belts are also less desirable for electrophotographic imaging systems because the seam forms a weak point in the belt and collects toner debris during cleaning, particularly with wiper blade cleaning devices. The seam and wiper blade interaction also causes a disruption in motion quality which impacts registration and timing in applications where multiple images must be closely referred to each other.
Electrodeposition of polymer films from polymer emulsions is known in the industry and is used for applying polyamide-imide and other similar coatings on hard to coat objects such as wire windings of motors and transformers. The polymer emulsions used in this type of process are rather dilute, resulting in slow deposition rates which limit practical film thicknesses to about 76 micrometers (3 mils) or so. Also, these polymers adhere very well to metal surfaces and are not readily removable from metal surfaces to obtain a free standing film. Curing of these coatings is a problem because they contain low boiling solvents which must be slowly removed to prevent bubbling of the coating. This requires special programmed ovens and slow drying conditions. Also, replenishment of the depleted polymer portion of coating emulsions is diffult. Moreover, the number of coated articles per batch of dispersion material is limited. Further, the reclaiming of solvent for the emulsions is complex and expensive. In addition, the total cost per coated article is high.